The present invention relates to a diversity system provided with diversity channels, each of the diversity channels having a unit provided with a printed circuit board and a circuit description element in which an electric circuit described in a hardware description language is implemented. The present invention also relates to a producing method of such a system.
A digital signal processing approach using LSI, such as CPU or FPGA (Field Programmable Gate Array), may be applied to a radiation monitoring device of a safety protection instrumentation system for a nuclear plant. The digital signal processing can make it possible to deal with more complicated calculation, and has more accuracy and higher resistance to noise than an analog signal processing. Also, it becomes easier to make a system compact by applying the digital signal processing. Like these, there are many advantages in application of the digital signal processing. However, there also exists a disadvantage peculiar to the digital signal processing that an error may occur at a certain timing of signal processing or under a certain condition.
The safety protection instrumentation system has an important role on nuclear reactor protection. This role is represented by judging a scrum of the nuclear reactor at abnormalities and outputting a signal of scrum. Therefore, it is necessary to multiplex instruments and to be designed so as not to start an incorrect operation or not to remain incorrectly in non-operation. In order to apply the digital signal processing to such a safety protection instrumentation system, a quality assurance activity is necessary through a design phase and a manufacturing phase. Also it is necessary to validate the instruments by verifying and extracting causes of the above-mentioned incorrect operation and incorrect non-operation through the design phase or a pilot phase.
On the other hand, for the safety protection instrumentation system equipped with FPGAs can be constituted as a hard-wired logic. Consequently, as compared with a CPU based system where software mainly controls, the processing is decisive and the processing operation is also deterministic generally. Therefore, there is a merit of easy verification. However, since the digital signal processing is applied, the error resulting from the design logic error or the signal processing timing still exists. Therefore, a safety protection instrumentation system equipped with FPGAs which can eliminate those factors has been invented (for example, refer to Japanese Patent Application Publication 2005-249609; the entire content of which is incorporated herein by reference).
Generally, a safety protection instrumentation system is configured as a diversity system. About FPGA applied to such a safety protection instrumentation system, the means of verification of a design, an action, and a signal processing timing, etc. and validation have been proposed. However, as a potential problem, an artificial error in a design phase, a defect of an FPGA element, or a defect of FPGA configuration tools, such as, a logic synthesis tool of FPGA, can be a cause of malfunction common in the diversity system. If a cause of malfunction common to all diversity channels exists, each of the diversity channels may malfunction simultaneously because of the common cause, and the whole diversity system may malfunction.